Recently, there has been a substantial level of interest in minimally invasive and percutaneous replacement of cardiac valves. In the specific context of pulmonary valve replacement, U.S. Patent Application Publication Nos. 2003/0199971 A1 and 2003/0199963 A1, (Tower et al.), which are incorporated herein by reference in their entireties, describe a valved segment of bovine jugular vein mounted within an expandable stent, for use as a replacement pulmonary valve. The replacement valve is mounted on a balloon catheter and delivered percutaneously via the vascular system to the location of the failed pulmonary valve and expanded by the balloon to compress the valve leaflets against the right ventricular outflow tract, anchoring and sealing the replacement valve. The valve is also useful to replace failed pulmonary valves located in valved conduits.
U.S. Pat. No. 5,411,552 (Andersen et al) discloses a percutaneously deliverable valve for aortic valve replacement. Like the Tower et al. valve, this valve system employs a stent external to the valve to exert pressure against the vessel at the implant site to provide a seal. This pressure of the stent against the vessel also helps to keep the valve from becoming displaced once it has been implanted. With these and other percutaneously delivered valves, the stent or other expandable member is typically designed to surround at least the valve orifice. This basic configuration allows blood to flow through the center of the valve when the valve is open, with the multiple valve leaflets sealing against themselves to close the valve. Because the native aortic valve annulus in which the replacement is to be implanted may be calcified and have an irregular perimeter, this basic configuration can be problematic, particularly in the context of replacement aortic valves. For example, a valve annulus with an irregular perimeter can make it difficult for an expanded stent to accurately follow the contours of the native annulus, which can result in peripheral fluid leakage. This problem is typically not present in traditional surgically implanted valves, since their relatively rigid stents are typically sealed to the valve annulus with a sealing ring that is attached to the annulus by means of numerous sutures.
Other procedures and devices that have been developed include, for example, surgically implantable valves disclosed in U.S. Pat. Nos. 4,339,831 (Johnson) and 5,449,384 (Johnson), both of which are incorporated herein in their entireties. These valves have a configuration that is essentially the opposite of the natural configuration, such that the valve leaflets open inwardly and close by expanding outwardly to contact the native aortic valve annulus. These valves further include a framework comprising a plurality of struts that are sutured to the patient's annulus or an artificial annulus reconstruction ring and a flexible membrane attached to the framework to allow the membrane segments or leaflets to freely open inward to allow forward blood flow through the valve. Although the struts are described as being flexible, these valves are not contemplated to be implanted percutaneously due to the need to physically suture these implantable valves to the annulus of a patient. Another type of valve that was developed is described in U.S. Pat. No. 3,671,979 (Moulopoulos). This reference discloses a valve that can be inserted, withdrawn and retained relative to its desired implanted position with the use of a catheter. A membrane of the valve expands outward like an umbrella to seal against the interior of the aorta, downstream of a damaged aortic valve, and collapses and enfolds the catheter to allow flow of blood when the valve is open. However, this valve is not capable of being retained in this position and functioning as a valve without the use of its catheter.
There is a continued desire to provide cardiac valves that can be implanted in a minimally invasive and percutaneous manner, while minimizing or eliminating paravalvular leakage.